A typical rotary power tool includes a housing, a motor supported by the housing and a spindle rotatably supported by the housing and selectively driven by the motor. A tool holder, such as a chuck, is mounted on the forward end of the spindle, and a tool element, such as a drill bit, is mounted in the chuck.
To assist the operator in removing and/or supporting the tool element in the tool holder, the power tool may include a spindle lock for preventing rotation of the spindle relative to the housing when a force is applied by the operator to the tool holder to remove the tool element. The spindle lock may be a manually-operated spindle lock, in which the operator engages a lock member against the spindle to prevent rotation of the spindle, or an automatic spindle lock, which operates when a force is applied by the operator to the tool holder.
There are several different types of automatic spindle locks. One type of automatic spindle lock includes a plurality of wedge rollers which are forced into wedging engagement with corresponding wedge surfaces when a force is applied by the operator to the tool holder. Another type of automatic spindle lock includes inter-engaging toothed members, such as a fixed internally-toothed gear and a movable toothed member supported on the spindle for rotation with the spindle and for movement relative to the spindle to a locked position in which the teeth engage to prevent rotation of the spindle.
To accommodate such automatic spindle locks, some rotational play or movement may be provided between the spindle and the driving engagement with the motor. The spindle lock operates (is engaged and disengaged) within this “free angle” of rotation between the spindle and the driving engagement of the motor.
One independent problem with the above-identified automatic spindle locks is that, when the motor is switched from an operating condition, in which the spindle is rotatably driven, to a non-operating condition, the inertia of the still-rotating spindle (and tool holder and/or supported tool element) causes the automatic spindle lock to engage to stop the rotation of the spindle relative to the motor within the free angle of rotation between the spindle and the motor. The engagement of the spindle lock can be sudden, causing an impact in the components of the spindle lock, resulting in noise (a big “clunk”) and, potentially, damage to the components.
This problem is increased the greater the inertia acting on the spindle (i.e., with larger tool elements, such as hole saws). With the high-inertia tool elements, the spindle may rebound from the impact (of the spindle lock engaging), rotate in the opposite direction (through the free angle of rotation) and impact the driving engagement with the motor, and rebound (in the forward direction) to re-engage the spindle lock. Such repeated impacts on the spindle lock and between the spindle and the driving engagement of the motor causes a “chattering” phenomenon (multiple noises) after the initial impact and big “clunk”.
Another independent problem with existing power tools is that, when the motor is switched from the operating condition to the non-operating condition, a braking force may be applied to the motor while the spindle (under the force of the inertia of the spindle (and tool holder and/or supported tool element) continues to rotate through the free angle. The braking of the motor. (coupled with the continued rotation of the spindle) causes the automatic spindle lock to engage resulting in noise (a big “clunk” and/or “chattering”) and, potentially, damage to the components.
The braking force applied to the motor can result from dynamic braking of the motor, such as by the operation of a dynamic braking circuit or as results in the operation (stopping) of a cordless (battery-powered) power tool. In other words, when the motor is stopped, the difference between the force rotating the spindle (the inertia of the spindle (and tool holder and/or supported tool element) and the force stopping the motor (i.e., whether the motor coasts or is braked) causes the automatic spindle lock to engage. The greater difference in these oppositely acting forces, the greater the impact(s) (a big “clunk” and/or “chattering”) when the spindle lock engages.
U.S. Pat. No. 7,063,201 describes a power tool with a spindle lock that addresses these problems. The spindle lock includes a spring and a detent arrangement to control and buffer the rotation of the spindle and to delay the engagement of the locking elements in both forward and reverse operation. Multiple spring members may cooperate to apply a force to delay the operation of the spindle lock. However, one of the drawbacks that have been found to occur with this spindle lock is that the amount of delay can be variable. In addition, when producing a model range of power tools, it is advantageous to use common parts as far as possible, however with this old tool it has been difficult to readily vary the delay by changing the spring members alone, without a need to also alter the mutually engaged component parts. It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or more generally to provide an improved spindle lock.